Fin arrangement for a projectile



y 1957 J. R. JASSE 2,793,591

FIN ARRANGEMENT FOR A PROJECTILE Filed Dec. 17, 195.4 2 Shets-Sheet 1 9%vawdwr: jaw JR Raymw z y 1957 J. R. JASSE FIN ARRANGEMENT FOR A PROJECTILE 2 Sheets-Sheet 2 Filed Dec. 17, 1954 FIN ARRANGEMENT FOR A PROJECTILE Joseph Raymond Jasse, Paris, France, assignor to Societe Nouvelle des Etablissements Brandt, Paris, France, a French body corporate Application December 17, 1954, Serial No. 475,973

Claims priority, application France December 21, 1953 3 Claims. (Cl. 102-50) The present invention relates to the guidance of projectiles and in particular self-propelled projectiles or rockets.

It has for an object to provide an improved fin arrangement for a projectile which permits an excellent guidance of the latter without disturbances While being simple in construction and faultless in operation.

Another object of the invention is to provide a fin arrangement which is of the type having fins that are opened by a pivotal movement on their common support about axes parallel to the longitudinal axis of the fin arrangement and which is characterized in that said fins have a generally cylindrical shape and such cross-section that when they are folded or closed against their support the fin arrangement forms a unit having a cylindrical outer shape and a circular cross-section.

Another object of the invention is to provide a projectile in which this fin arrangement is incorporated, the latter having such dimensions that in the position thereof in which the fins are closed the cylinder formed by these fins has substantially the same outer diameter as the cylindrical part of the body of the projectile.

Further features and advantages of the invention will be apparent from the ensuing description.

In the accompanying drawings given merely by way of example:

Fig. 1 is a rear end view of a fin arrangement which is in its open or deployed position and is combined with a self-propelled projectile, the body of the fin arrangement constituting the ejection nozzle for the propelling gases;

Fig. 2 is a plan view thereof, the fin arrangement and the projectile being shown disposed horizontally;

Fig. 3 is a view similar to that shown in Fig. 1 but in which the fins are closed or folded back;

Fig. 4 is a corresponding plan view;

Fig. 5 is a sectional view on line 55 of Fig. 3, and

Fig. 6 is a diagrammatic view on a very small scale of the projectile which has its fin arrangement closed or folded back and is in place in the launching tube.

According to the illustrated embodiment, the fin arrangement is adapted to be fixed to the rear end of the cylindro-ogival body 1 of a self-propelled projectile or rocket.

This fin arrangement comprises the combination of a support S and three fins A pivoted tothesupport for pivotal movement about axes parallel to the longitudinal common axis XX of the fin arrangement and the projectile itself.

The support S is a body of revolution about the axis XX; it comprises at the forward end, relative to the direction of flight, a screw-threaded portion 2 for the purpose of its attachment to the rear end of the body 1. The shoulder 3 adjacent the screw thread has a diameter d (Fig. 2) whichis very slightly less than the outer diameter of the body 1. The'support S is provided with an axial throughway aperture which forms a passageway 4 for the ejection of the propelling gases. The rear part of this 2,793,591 Patented May 28, 1957 sit passageway is divergent and is followed by a short cylindrical or parallel portion 5 in which is secured a ring 6 provided with inclined fins 7. The latter are adapted to cause the projectile to rotate in the direction of arrow f (Fig. 1) about its longitudinal axis.

Externally, the support S comprises near the front end behind the shoulder 3 a recess or rebate forming a cylindrical support surface 8. From this support surface the support decreases rapidly in diameter down to a cylindrical surface 9 which is connected by a flared portion 10 to a rear flange 11 which comprises as many bosses 12 as there are fins A; these bosses are angularly equispaced.

Fitted in each boss 12 is a spindle or pin 13 which ex- -tends in a direction parallel to the axis XX and is adapted to serve as a pivot pin for the corresponding fin A. This --pin extends through a lug 14 integral with the support S and its forward end is also engaged in a blind hole 15 formed in the support (Fig. 5). Each pin 13 is held in position in the longitudinal direction relative to the support by for example giving a blow with a centre punch "between the rear part of the pin 13 and the boss 12.

One fin A is pivotably mounted on each rod 13. The

"three fins A are identical and are of metal or light alloy such as Duralumin. Each fin comprises a thin wall having the general shape of a segment of a cylinder and an armate cross-section the concave side of which faces the direction of rotation of the projectile (Fig. 1). It com prises, starting from the pivot pin, two portions 16 and lTconnected by a rib 18.

The portion 16 has an outer radius equal to the inner :radius of the portion 17. These radii being equal to where e is the thickness of the portion 17 (Fig. 1). The

.portion 16 is provided with two eyes 19 and 20 pivotably mounted on the pin 13. These eyes and the portion 16 are reinforced by inner ribs 21. The latter also perform another function to be explained hereinunder.

The rear eye 19 includes a notch 22 (Figs. 2 and 5) .whioh isso positioned and oriented with respect to the corresponding fin as to engage, in the open position of the latter (Figs. 1 and 2), a locking projection 23 constituting an abutment of prismatic or like shape and carried by the forward face of the boss 12. The other eye 20 is so disposed relative to the lug 14 and the recess 8, as to per- .mit such longitudinal displacement of the fin as to enable the notch 22 to engage with (Fig. 2) or disengage from (Fig. 5) the abutment 23.

The portion 16 of the fin has such length that in the .two positions thereof its rear edge 24 is disposed slightly beyond the end of the support S whereas its front edge 25 is at the level of the front end of the eye 20.

The other portion 17 of the fin has the following characteristics:

. a. Its arcuate cross-section is such that its outer radius is substantially equal to t b- Its-rear edge 26 is in alignment with the edge 24 of the portion 16.

0. Its front edge 27 is disposed in front of the edge :25 of the portion 16 so that in the closed position of the limit bears against the recess 8 of the support S.

d. :It comprises two apertures 28 which are in line with ".the eyes 19 and 20- in the closed position of the fin.

.The fin arrangement is completed by a-spring 29 for each fin. This spring is adapted to open the-fin by causing it to pivot about the pivot pin 13 in the direction of arrow f (Fig. 3) and, furthermore, to displace the fin in the longitudinal direction in the direction of arrow f (Fig. 5) so that it engages the abutment 23.

This spring 29 is of the helical type and encompasses the pin 13 between the lug I4 and the eye 19. It Works under torsion in the direction of the pivotal movement of the fin, since a branch 30 and two ends 31 and 32 formed thereon bear against the support S and the fin respectively. Furthermore, it works under compression in the longitudinal direction between the lug 14 and the eye 19.

A removable strap 33 is provided for maintaining the fins in their closed, folded position in opposition to the action of the springs 2? (Figs. 3 to 6). V v

In this closed position, the fins A bear against the recess 8 and the portion 17 of each fin overlaps the portion 16 of the adjacent fin situated in front thereof relative to the direction of rotation of the projectile. The fin arrangement forms, therefore, a cylindrical unit having substantially the same outer diameter d as the body 1 of the projectile. Only the strap 33 projects from this body.

Thus,'when the projectile is engaged in the tube T (Fig. 6) of the launching apparatus, the strap 33 abuts the rear end of this tube and as soon as the projectile is launched this strap is wrenched off and the fins are freed. These fins remain temporarily closed while they are still inside the tube T and they are therefore effective in guiding the projectile.

As soon as the fin arrangement issues from the tube T the springs 29 and all the fins instantly open. As all the fins open in a strictly identical manner, the projectile is not disturbed on its trajectory.

When the fins are completely open the notches 22 engage the abutments 23 which, on account of their prismatic or like shape, automatically take up any play. The fins A are thencefo'rth securely locked in. position and, owing to their stiffening ribs, they are not subject to any vibration capable of disturbing the projectile. They behave exactly as though they were integral with their'support S.

As will be understood, these fins present as large a stabilizing surface to the surrounding air as would be prlnssible with a folding fin for a given calibre of projecti e.

Apart from their reinforcing function, the inner ribs 21 cause an increase in the air resistance and a thinning of the boundary layer, which results in a steeper slope of the aerodynamic moment curve as a function of the incidence, which is a favorable phenomenon as concerns the stability of the machine.

Experiments have demonstrated that these fins are indeed very efiicient and that firing precision is thereby considerably improved.

Although a specific embodiment of the invention has been described hereinbefore it is to be understood that many changes and modifications may be made therein without departing from the spirit of the invention or th scope of the appended claims.

Having now described my invention what I claim as new and desire to secure by Letters Patent is:

1.'In a fin arrangement for a projectile; a support comprising at least one outer support surface; a plurality of parallel pivot pins carried externally by said support; locking means on said support at one end of each of said pivot pins; fins each of which is mounted -'on one of said pivot pins in such manner that each fin is capable of pivoting about its corresponding'pivot pin between an operative open position and an inoperative closed position in which latter position it is closed onto said support surface and furthermore capable of slid ing along said pivot pin between a locked position in which said fin is engaged by its corresponding locking means and an unlocked position in which it is disengaged from said locking means, the locked position corresponding to the operative position and the unlocked position to the inoperative position; and as many single elastically yieldable means as there are fins, each of said yieldable means being adapted constantly to urge its corresponding fin to pivot about the pivot pin in a direction which tends to bring it into said said open operative position and to furthermore urge the fin along its pivot pin in a direction which tends to bring the fin to said locked position.

2. In a fin arrangement for a projectile: a support comprising at least one outer support surface; a plurality of parallel pivot pins carried externally by said support; locking means on said support at one end of each of said pivot pins; fins each of which is mounted on one of said pivot pins in such manner that each fin is capable of pivoting about its corresponding pivot pin between an operative open position and an inoperative closed position in which latter position it is closed onto said support surface and furthermore capable of sliding along said pivot pin between a locked position in which said fin is engaged by its corresponding locking means and an unlocked position in which it is disengaged from said locking means, the locked position corresponding to the operative position and the unlocked position to the inoperative position and as many helical springs as there are fins, each of said helical springs being interposed in the longitudinal direction between its corresponding fin and the support so that this spring is under compression and urges the fin in axial translation toward said locked position, this spring being provided with at least two radial branches one of which bears against the support and the other against the fin so that this spring is also under torsion and urges the fin to pivot toward said open operative position.

3. In combination: a projectile having a body at least the rear part of which has an outer surface having an axis coinciding with the longitudinal axis of said body and a fin arrangement fixed at the rear of said body and comprising a support fixed to the latter and fins pivotably mounted on said support for pivotal movement about pivot pins parallel to the axis of said body, each of said fins having a thickness which is at least substantially constant and having a general shape of a segment of a cylinder the generatrices of the latter being parallel to said axes and the cross-section of each fin subtending an. angle at the centre of the projectile which is greater than that subtended by the pivot pins of two adjacent fins, whereby the fins partially overlap one another in their inoperative position closed against said support, each fin comprising in the circumferential direction of the projectile two portions of a cylinder whose arcuate cross-sections have different radii, one of these portions, by which the fin-is pivotably mounted on the support bcing reinforced 011 its inner face by ribs and having an outer radius which corresponds to the inner radius of the other portion, the outer radius of the latter corresponding to half the outer diameter of said rear part of the projectile, whereby when the fins are closed against. said support the fin arrangement assemblage References Cited in the file of this patent I V UNITED STATES PATENTS 1,890,175

Brandt Dec. 6, 1932 2,421,752 Jones n June 10, 1947 2,465,401 Skinner Mar. 29, 1949 f FOREIGN PATENTS 494,610 France June 3, 1919 514,085 Great Britain Oct. 30, 1939 9l4,933 Germany July 12, 1954 

